Optimization of growth and food efficiency are of primary importance in livestock animals raised for meat.
Effective growth promoting zootechnical compositions are available, including the steroids estradiol and melengestrol acetate (MGA), trenbolone acetate (TBA), zeranol, and testosterone and other non-steroidal compounds e.g. zilpaterol, ractopamine, ionophore antibiotics, probiotics.
Similarly, estrus-related reduction of appetite in female livestock animals diminishes weight gain. U.S. Pat. No. 3,417,182 discloses the use of MGA for the control of estrous periods and the stimulation of growth for domestic birds and animals.
Some of these growth promoting zoo-technical compositions are administered via the feed to the livestock animals, e.g. zilpaterol hydrochloride and melengestrol acetate
Some of these compositions are implantable in animals. Such implantable compositions are often administered as solid compressed pellets which are injected by an implanter equipped with a hypodermic needle. In livestock, implants are normally inserted in the ear or in other areas of the animal that are not for consumption and are discarded. The implanter needle is used to make a small self-sealing implant-receiving puncture beneath the skin at a suitable location on the body of the animal. Small pellets of a composition are forced through the needle and left under the skin as the needle is removed.
For example, TBA has been used in the form of an implantable composition with heifers, lambs, pigs, etc. to increase body weight gain in livestock as disclosed in U.S. Pat. No. 4,472,394. U.S. Pat. Nos. 4,900,735 and 5,147,869 disclose implantable compositions comprising TBA (TBA) and estradiol used to generate improved growth characteristics in feed lot cattle.
In the prior art it is stated that it would be desirable that one or more growth stimulating agents and one or more supplemental agents could be mixed together and incorporated in a single pellet for implantation; however, because each of the agents may be absorbed at different rates or require different carriers, normally there will be a different pellet, such as for each of the agents.
It would be desirable to identify a veterinary drug delivery system for release of two actives from the same compartment that allows for independent adjustment of this release from the device for compounds that are partly present in crystalline form.
Furthermore, there is a need for a system which releases both a growth stimulating dosage in combination with other compounds that improve the zoo-technical performance e.g. parasiticidal dosage, an antimicrobial dosage, an estrus suppressant dosage and/or other supplemental agents to provide control of parasites, microbial infection, estrus and maximize growth rate.
It is therefore the object of the present invention to provide a zootechnical drug delivery system in which the release rate of the two compounds that are partly present in the solid state and partly in the dissolved state can be regulated independently from one another from the same compartment.